The production of semiconductor devices such as photoinput sensor devices, photosensitive devices for electrophotography, photovoltaic devices, liquid crystal driving circuits, etc., has caused a great demand for forming a deposited film over a large area at a reduced cost.
Heretofore, for forming a deposited film using a gas phase growing method, it is known that a deposited film of large area can be formed by using plasma, heat, light, etc. as the energy for decomposing a film-forming raw material gas. A single film-forming raw material gas is seldom used in any case. A dilution gas is usually used in addition to the film-forming raw material gas even in the case where a deposited film comprising a single component is to be formed. In addition, in the case of forming a deposited film comprising a plurality of constituents by the gas phase growing method, a gaseous mixture comprising a plurality of film-forming raw material gases is generally introduced into a film-forming chamber.
However, any of the conventional deposited film-forming methods involves the following problems:
Initially, even in the case where a deposited film comprising a single component is to be formed, various film-forming parameters have to be optimized, including the mixing ratio between the film-forming raw material gas and the dilution gas, in order for the resulting deposited film to be provided with desired properties. In this case, the allowable ranges for the film-forming parameters are relatively narrow. Further in the case of forming a deposited film comprising a plurality of constituents, a plurality of film-forming raw material gases for the respective film-constituents have different levels of decomposing energy. Accordingly, various film-forming parameters such as flow rate ratios among the film-forming raw material gases to be introduced into the film-forming chamber are often more restricted in comparison with depositing a film of a single component. In addition, there is also a problem that it is rather difficult to change the flow rate ratios so as not to reduce the quality of the film to be obtained.
Further, upon decomposing said plurality of film-forming raw material gases, various relevant conditions have to be controlled in a delicate manner and, accordingly, controllable ranges for the film property and the film composition are also to be limited.
In order to overcome the foregoing problems, a method has been proposed to subject each of a plurality of film-forming raw material gases to the action of an activation energy, independently in a respective activation chamber situated separately from a film-forming chamber; subsequently introducing each of the resultant activated film-forming raw material gases separately into the film-forming chamber, mixing and reacting them with each other to thereby cause the formation of a deposited film on a substrate therein (see, for example, Japanese Patent Laid Open Publication No. ho.61(1986) 179869. According to this method, the activation of the respective film-forming gases can be controlled independently. Because of this, it is possible to extend the range of the film-forming parameters for improving the film property when forming a film comprising a single component. It is also possible to provide film-forming parameters in a wide range wherein the desired quality of the resulting deposited film is ensured as is the case when forming a deposited film comprising a plurality of constituents.
However, in regard to the apparatus for practicing the foregoing later film-forming method, there is difficulty in forming a deposited film over a large area as compared with the apparatus for practicing the foregoing prior method for forming a deposited film using a gas mixture.
That is, with respect to the conventional method, it is possible to form a deposited film having a large area as long as the decomposing energy can be evenly applied over a wide range onto the gaseous mixture, thereby resulting in the formation of a deposited film on a substrate having a large area. The related film-forming parameters may then be properly adjusted in the film-forming chamber.
However, in the case of the foregoing later method, the respective film-forming raw material gases are firstly activated separately in respective activation chambers situated separately from the film-forming chamber before the respective resultant activated film-forming gases are separately introduced into the film-forming chamber and mixed and reacted with each other. A deposited film is thereby formed on a substrate therein. Unevenness is apt to occur in the thickness and/or the quality of a deposited film thereby obtained. Because of this, it is extremely difficult to form a desirable deposited film having a large area which is uniform in thickness and of high quality by using this method. A typical apparatus suitable for practicing this method is one provided with a plurality of nozzle or ring-like gas-liberating ports as shown in FIG. 25. In the practice of this method, using the apparatus as shown in FIG. 25, unevenness is apt to occur in the thickness and the quality of a deposited film obtained because of differences in the distances between said plurality of nozzles or ring-like gas-liberating ports. Thus, this method is unsatisfactory for forming a desired deposited film having a large area and which is uniform in both thickness and quality.